Structural and functional studies will be carried out in order to provide a molecular-level understanding of the role of heme proteins in fundamental physiological processes, including respiration metabolism, and the regulation of cellular responses. Resonance Raman spectroscopy will be applied as a structural monitor of the heme group, and of its interaction with proteins and with exogenous ligands, including especially the newly discovered signaling molecule NO. Computer modeling with a high quality force field will be employed in order to extract maximum information from the spectra.